Wednesday, January 6, 2010

Steller Sea Lion, endangered

George Wilhelm Steller, a German naturalist, accompanied Vitus Bering, a Russian explorer, on his second Alaskan expedition in 1741. Mr. Steller was the first qualified observer to study and classify these northern sea lions. Thus the name Steller Sea Lion.

The world population is divided into two groups, the western stock and the eastern stock. This division occurs at 144 degrees W longitude (Cape Suckling) just east of Prince William Sound, Alaska. The western stock can be found in the North Pacific Ocean from northern Hokkaido, Japan through the Kuril Islands, Okhotsk Sea, Commander Islands in Russia, the Aleutian Islands and central Bering Sea. The eastern stock live off the southern coast of Alaska and south to the Channel Islands of California.

Steller Sea Lions spend time on land on offshore islands. Some are called rookeries where the females and pups live. The other islands are called haul-offs. The rest of the time is spent in the water hunting for food. Their main diet is composed of a wide variety of fishes, squid, and octopus. Some of the most important prey species in Alaskan waters include walleye, pollock, Atka mackerel, Pacific herring, capelin, Pacific sand lance, Pacific cod, and salmon. These sea lions have rear flippers that can rotate to help them waddle on land and they have external ear flaps. Their lifespan can be as long as twenty-three years. Males can weigh up to 2,400 pounds and be ten to eleven feet long. Females can weigh about a thousand pounds less and be seven to nine feet long. Females give birth to a single pup after a year long gestation period. Native predators are killer whales ( orcas) and white sharks.

Populations have dropped drastically within both the western and eastern stocks off the coast of Alaska and down the continental United States and Canada in the past thirty years. Exact reasons for the decline are not known but researchers believe that increased commercial fisheries are catching large numbers of the Steller Sea Lion prey. Drownings occur also when sea lions become entangled in the fishing nets. Pollock is the major prey fish consumed by the western stock. Current distribution of the Pollock fishery overlaps extensively with the distribution of foraging sea lions and their habitat. Commercial fishing for pollock within these waters increases during the fall and winter which further stresses the sea lions because their metabolic demands are greater at this time. Nursing females and young lean sea lions are most vulnerable during the harsh winter season. When Steller's have to swim further out to sea in search of food they are increasingly exposed to predation.

The Eastern stock has its own tale of woe. Open sea salmon farm pens all along the Pacific coast are cropping up in sea lion habitat. Shortages of herring, hake, and pollock as a food source has driven the sea lions to invade the salmon nets. In the past, salmon farmers have shot and killed thousands of marine mammals, including Stellers. Thankfully now the Steller sea lion is protected under the Endangered Species Act though this act does nothing to slow the commercial fisheries invasion of the Steller sea lion habitat.